The BCMV is the most widespread viral disease. It causes some of the most economically important diseases of legume crops around the world. Plant infection may reach 100% in fields and yield losses range from 6 to 98% depending upon the cultivar and time of infection. It is economically important throughout Africa, Europe, North America and Latin America.

Symptoms

The type of symptom produced is determined by the strain of BCMV, temperature and the host genotype. The BCMV may incite three types of symptoms: mosaic, systemic necrosis (black root), or local lesions or malformation. Symptoms associated with common mosaic include leaf rolling or blistering, light and dark green patches on the leaf (green mosaic), chlorotic vein banding, yellow mosaic and growth reduction. Mottling and malformation of the primary leaves is an indication that the primary infection occurred through seed. Cultivars which develop common mosaic may have distinct chlorotic or necrotic local lesions which are not associated with the vascular system. Systemically infected plants may have smaller and fewer pods and infected pods may sometimes be covered with small, dark green spots and mature later than uninfected pods. Black root is characterized by local necrotic lesions which extend into the veins causing systemic necrosis in the vascular system; this symptom only occurs in cultivars possessing the dominant resistance gene I. This necrosis can extend into the roots, stem and meristem and may result in plant death if the plant is infected at an early stage. Leaf distortion and blistering, dwarfing, downward curling of leaf margins, vascular necrosis, light and dark green mosaic, ring shaped and pin-point local lesions, distortion of flowers and buds.

The virus is probably distributed worldwide (in Phaseolus beans wherever they are grown).

Biology and transmission

Virus is of the genus Potyvirus in the family Potyviridae. Filamentous particles are about 750 nm long and 15 nm wide. Virus is transmitted by mechanical inoculation (sap), transmitted by seeds (up to 83% in Phaseolus vulgaris and from 7 to 22% in tepary bean, transmitted by pollen to seed. The virus is transmitted by arthropods, by insects of the order Hemiptera, family Aphididae; Acyrthosiphon pisum, Aphis craccivora, A. fabae, Myzus persicae and other species. The virus is transmitted in a non-persistent manner. Bean common mosaic is caused by two species of the genus Potyvirus: Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV).

This virus affects bean in Africa, Australia, United States and Latin America.

Biology and transmission

The virus is of the Potyvirus genus in the Potyviridae family. The capsid is filamentous, flexuous with a clear modal length with a length of 740-750 nm. The virus is transmitted by mechanical inoculation; transmitted by seeds 0.02-2% in Arachis hypogaea; to 1% in Phaseolus vulgaris and to 0.008% in Vigna unguiculata (Demski et al., 1983), but not in Glycine max, Pisum sativum and Cassia obtusifolia. the virus is transmitted by arthropods, by insects of the order Hemiptera, family Aphididae; Aphis craccivora, A. gossypii, Hyperomyzus lactucae, Myzus persicae and Rhopalosiphum padi. The virus is transmitted in a non-persistent manner (A. craccivora can remain infective for 2 hours and M. persicae for 12 hours after acquisition (Paguio and Kuhn, 1974). Seed transmission in peanuts and beans, mottle and necrosis in peanut, bean and pea, Arachis glabrata resistant.

BSMV is undoubtedly the most widely distributed of the beetle-borne viruses which infects beans. It is considered to be economically important on a global sacale. The virus can reduce bean yields as much as 83 to 94 % reducing the amount and weight of seed produced by infected plants.

Symptoms

In Phaseolus it can induce diverse symptoms such as mosaic, or mottle, rugosity, epinasty, vein yellowing, stunting, and necrotic local lesion, depending on the variety inoculated.

The virus was first observed in southern United States and now is present in all the main bean producing nations of the world. The virus spreads in Africa, North America, South and Central Americas, France and Spain.

Biology and transmission

SBMV is a type member of the sobemovirus group which characteristically has isometric particles 28 to 30 nm in diameter and contains one molecule of positive-sense single-stranded RNA. The virus is transmitted by a vector. The virus is transmitted by sap, mechanical inoculation, grafting, seeds 3-7% in V. unguiculata cv.; it is transmitted by pollen to seed and transmitted by pollen to the pollinated plant. The virus is seed-borne and can be carried both in the embryo and as a contaminant on the seed coat. This virus, however, becomes inactivated upon the dehydration or storage of contaminated seeds. Secondary transmission occurs naturally by several species of chrysomelid beetles such as Cerotoma facialis, C. trifurcate and Epilachna varivestis. The virus is transmitted in a semi-persistent manner.

Detection/indexing method in place at CIAT

ELISA with commercial kit.

Treatment/control

Virus free seed, grown in areas where the virus does not occur, should be used.